In recent years systems have been devised which record information on a storage medium and provide a subsequent reproduction of the information from the storage medium. For the recording of high frequency information, such as video information, the systems now in use generally employ magnetic tapes as the storage medium. These tapes have proved fairly successful in recording signals representative of information and in obtaining the reproduction of the information. However, the magnetic structure of the tape limits the fidelity of the recording and reproduction so that the magnetic tapes have to be manufactured with considerable precision. The information recorded on the magnetic tapes also has a limited density of information so that a relatively great amount of tape is required to store information such as that required for a television program having a duration of one-half an hour or an hour. The limited density of information packing on the tape has resulted from limitations in the speed of response of the magnetic transducer heads which are disposed in contiguous relation to the tape.
In the systems now in use, a transducing head is generally disposed adjacent to the tape to record information in magnetic form on the tape and to reproduce the magnetic information as electrical signals from the tape. The adjacent relationship between the transducing head and the tape occasionally causes the tape to rub against the head so that magnetic particles become removed from the tape and deposited on the head to effect the operation of the head. The magnetic particles on the tape tend to produce an abrasive action on the head, thereby permanently affecting the response characteristics of the head.
It is also disadvantageous to use a magnetic tape as a master for the reproduction of a large quantity of data because of the considerable length of tape required for the master. It would, therefore, be more desirable to use discs as the master since they tend to store information in a more compact form than tapes. The disc systems of the prior art are generally of two types. In one system the light transmission characteristics of a spiral track in the discs is varied during the recording operation by an electron beam whose characteristics are controlled by signals representative of the video information to be stored. Reproduction of the signals from the disc is accomplished by directing a light beam at the disc and by modifying the light beam in accordance with the light transmission characteristics previously provided at successive portions on the spiral track of the disc. The modified light beam is detected to obtain a recovery of information previously recorded on the disc. This type of system is described in U.S. Pat. No. 3,361,873.
In another type of prior art system, a disc having a spiral track and a stylus similar to that used in high fidelity phonograph records is used. The information is recorded as vertical variations in the depth of the groove in a frequency-modulated form, and the stylus is coupled to a pressure transducer. Due to the abrupt trailing edge of the stylus, a pressure signal is detected indicative of the peak-to-peak spacing and hence the frequency modulated information.
Another type of readout device is the electrostatic pickup. This type of pickup is similar to the electrostatic pickup used in phonograph records wherein capacitive relief or a capacitor needle is used. The variation of the capacity of the needle or the instantaneous capacity at the peak in the track cause the oscillation frequency of a tuned circuit to vary above and below the normal mid-frequency, thereby resulting in a frequency modulated signal which is delivered to a suitable output circuit, as described in U.S. Pat. No. 2,423,208, and British Pat. No. 153,300.
The disc systems of the prior art have had certain important deficiencies; for example, the latter systems have a frequency response that may be too low to allow for a reasonable length of play time or for color encoding. In addition, the stylus constuction of those systems using capacitive relief is often very complicated, as disclosed in U.S. Pat. No. 2,423,208.